Expansion chambers for internal combustion engines are well known in the prior art. They may be attached to an engine as part of the exhaust system to achieve an increase in the power developed by the engine. In very small engines, for example, 0.21 cu. inch or 3.5 cc., even a modest increase in the power output of the engine is highly desirable.
In model boats powered by outboard methyl alcohol engines, expansion chambers are usually used to increase the power. One example of a commercially available expansion chamber is a K and B.RTM. "tuned pipe" manufactured by K and B Manufacturing of Downey, Calif. 90241. This device, which is very long and narrow when used on an outboard, is cantilevered from the end of the boat and thus has a long moment arm. This makes a boat equipped with this device "tail heavy" and disturbs the balance of the boat. It causes the front of the boat to come out of the water too far and tends to induce serious oscillatory actions.
Another prior art device somewhat similar to the above-mentioned K and B.RTM. device being made by K and B Manufacturing Company is the exhaust muffler with expansion chamber disclosed in U.S. Pat. No. 2,660,256 to WALKER. This device is also long and narrow, which causes it to have a long moment arm. Therefore, if such a device were installed on the back of a model boat, it would disturb the balance of the boat.
Still another muffler-expansion chamber which is long and narrow is disclosed in U.S. Pat. No. 3,462,947 to NOWAK. This device contains divergent and convergent cones overlying each other within a sleeve. The device also contains sound muffling baffles and a reflector plate to cause exhaust gases to reverse directions inside the sleeve. This NOWAK device also has a long moment arm. Therefore, if it were installed on a model boat engine, it would have the same disadvantages as the WALKER device described above.
A somewhat different type of expansion chamber used on small internal combustion engines, in this case model airplane engines, is a long, narrow U-shaped muffler with an attached expansion chamber, manufactured under the trade name Quadra-Charger by Cosmocon, Ltd., of Uxbridge, Ontario, LOC 1 KQ, Canada. This is tuned to be used with the Quadra.RTM. model aircraft engine.
One prior art device with some similarity to the above-mentioned Quadra-Charger device is shown in U.S. Pat. No. 4,186,819 to NOWAK et al. This device which was designed for snowmobile engines, is a U-shaped muffler with an attached expansion chamber. However, it contains a large and heavy baffle and appears to be too long and heavy for use on a model boat engine.
Another generally U-shaped combination muffler and expansion chamber is shown in U.S. Pat. No. 3,665,712 to TENNEY. This device has a complicated muffler arrangement with exhaust gases passing out of the expansion chamber into pipe 34, out apertures 37, across muffler chamber 35, into apertures 42, and out exhaust pipe 40. This arrangement was designed for use on a chain saw and is particularly well suited for preventing a chain saw operator from coming into contact with the exhaust system. However, it is obviously too heavy and complex for use in a very small internal combustion engine, namely, a model boat engine.
A somewhat different type of prior art device, a silencer for engines, is shown in U.S. Pat. No. 4,327,815 to HATTORI. This device has straight diverging and converging cones and a rotational mechanism (more specifically, a rotary pump equipped with a plurality of impellers) to function as a silencer. Again, for use on model boat engines, this device is too long, heavy and narrow and would disturb the balance of a model boat.
Still another type of prior art device is the elbow exhaust muffler disclosed in U.S. Pat. No. 2,682,312 to HOPKINS. This device is an elbow or plurality of elbows to be placed in the exhaust lines of large trucks. These elbows are equipped with ribs, transverse corrugations, and perforated baffles. Their primary function appears to be dissipation of heat and reduction of exhaust noises. Thus, the HOPKINS device would not be suitable for use as an expansion chamber on model boat engines.
A most important requirement of this expansion chamber for model boat operators is that it should definitely minimize balance upset of the boat hull. The boat driver should not be able to detect any difference between operation without or with an expansion chamber. The boat should not "feel" tail heavy or when in turns should not lead or lag the driver's radio commands due to the additional weight of an expansion chamber having its center of gravity located well off the main engine pivot. This extra weight and displaced center of gravity will change the moment arm which the radio servo mechanism must move. Also, this extra weight will place higher than normal inertia loads on the mechanism's mechanics, resulting in possible mechanical damage to the servo mechanism.
A performance goal that must be achieved by the model boat racer is the correct hull attitude relationship with the water when running at racing speeds. The hull should penetrate waves induced by other boats without nosing up or climbing the approaching wave front. If the boat noses up, the driver may have to throttle down to avoid flipping the boat. Additionally, the forward progress is slightly impaired since the boat is forced up and down due to the poor running attitude. If the boat attitude cannot be corrected by adjusting prop angle or prop height, the only means left is to add weight to the nose. Increasing the weight forces the boat to carry more payload and detracts from its performance.
A very popular boat used for general sport racing is a tunnel hull design. This design utilizes a catamaran type of hull which traps air between the sponsons to create a pressure pocket which lifts the boat to the planing position. When the boat's performance is increased by using a tuned pipe, this running attitude is even more sensitive. The reason for the increased sensitivity is additional air flow between the sponsons. Now, the boat will flip much more easily if the hull noses up. For these reasons, it is especially important that tunnel hull boats be properly balanced.
In view of the foregoing discussion, it should be apparent that the known prior art devices as mentioned above do not provide an expansion chamber which will meet the requirements of model boat racing enthusiasts for a compact expansion chamber with a very short moment arm. The ideal expansion chamber for model boating is one which will not upset a boat's balance by adding a long moment arm at the rear of the boat. The long moment arm causes oscillations, further causing the boat to bob up and down as it proceeds down its course. The boat may even turn over as its speed increases. Moreover, the long moment arm causes the nose of the boat to rise and capture excessive air. This makes it difficult to properly turn the boat. It also causes it to be hard to steer and makes it respond late to the radio controls.
Therefore, it is an object of my invention to provide an expansion chamber which has a short moment arm and which is lightweight and compact.
It is another object of my invention to provide an expansion which has a short moment arm and which is suitable for attachment to model boat engines.
It is a further object of my invention to provide an expansion chamber which does not disturb the balance of a model boat and which enhances the steering and thus provides a quick response to the radio controls.
It is a still further object of my invention to provide an expansion chamber which may be installed on a model boat without causing the model boat to oscillate at racing speeds, thus in turn causing the operator to have to throttle down.